OPTICAL POSITION DETECTING METHOD USING ASYNCHRONOUS MODULATION OF LIGHT SOURCE

In an optical position detecting method, a light beam is intensity-modulated with a given periodic waveform, and is then emitted from an object light source. An image sensor captures an image of the light source and stores corresponding image data per pixel. Subsequently, the image sensor is accessed successively at least four times at a pitch which is less than 1/4 of that of the periodic waveform, so as to read the image data per pixel to form a time-sequential data. Subsequently, a scalar product computation of the time-sequential data is executed using a reference waveform which is asynchronous with the periodic waveform while having a period relatively close to the period of the periodic waveform, so as to derive first scalar data. Another scalar product computation of the time-sequential data is further executed using an orthogonal waveform which is out of phase by 90.degree. relative to the reference waveform, so as to derive second scalar data. Finally, an image processing is performed using the first and second scalar data so as to extract a position of the light source.